In coating or deposition devices, dry etching devices, and others in a semiconductor manufacturing process, for example, special gases such as silane, corrosive gasses such as chlorine gas, combustible gasses such as hydrogen gas and phosphine gas, and so on are used. Gas flow rates of those gases directly influence the quality (good/bad) of products and thus have to be strictly controlled. Especially, in association with recent laminated and miniaturized structures of semiconductor substrates, a demand for high reliability of process gas supply systems has been increased.
Therefore, for example, Patent Documents 1 and 2 disclose techniques of controlling flow rates of gases to be supplied in semiconductor manufacturing processes.
Patent Document 1 discloses a technique to alternately operate a system in a flow mode and a no-flow mode to adjust a flow rate of gas batchwise flowing through a mass flow controller to a specified flow rate. Specifically, a flow line is provided in which a cutoff valve, a reference capacity (corresponding to a measuring tank), a pressure sensor, and a pressure regulating valve are arranged in series on an upstream side of the mass flow controller. An actual flow rate is determined based on pressure drop in the reference capacity and a set value of the mass flow controller is adjusted.
Patent Document 2 discloses a technique to accurately calculate a flow rate of process gas. Specifically, a cutoff valve, a known volume part (corresponding to a measuring tank) including a heat storage part, a pressure sensor, and a variable pressure regulating valve are arranged in series on an upstream side of a mass flow controller. An actual flow rate is calculated based on pressure drop in the known volume part, and the variable pressure regulating valve is corrected if the actual flow rate differs from a specified flow rate. When the pressure drop in the known volume part is measured in terms of time function, heat transfer from the heat storage part is conducted to keep a gas temperature constant.